急求GWD17-Q38分析

lzczjgsu · 发表于 2010-8-8 12:57:31

38. GWD17-Q38:

All Y chromosomes in existence today are descended from a single ancestor’s who is thought to have lived about 140,000 years ago.

A.a single ancestor’s who is thought to have lived

B.a single ancestor’s who was thought to live

C.a single ancestor whom it is thought had lived

D.the Y chromosome of a single ancestor who is thought to have lived

E.the Y chromosome of a single ancestor whom it was thought had lived

答案选择D，谁能分析下？为什么D中的完成时态是正确的，完成时不是不可以和years ago 连用吗？

everine · 发表于 2010-8-8 13:18:23

同问。。
不过其他选项错的更离谱些。。

急求GWD17-Q38分析

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